Motor speed controlling apparatus

ABSTRACT

An apparatus for controlling the speed of an electric motor, wherein use is made of an element sensitive to a pressure, the electrical resistance of said element or a voltage developed thereacross being varied in accordance with the pressure imparted thereto, and a centrifugal force produced by a rotary member is imparted to said sensitive element so that the speed of said electric motor is controlled in accordance with variations in the electrical resistance of said sensitive element.

United States Patent Sasabe et al.

MOTOR SPEED CONTROLLING APPARATUS Inventors: Kaoru Sasabe, lkeda-shi; Fi iio Oda, Ashiya-shi, both of Japan Assignee: Matsushita Electric Industrial Co.,

Ltd Osaka, Japan Filed: April 30, 1970 Appl. No.: 138,992

Related US. Application Data Continuation of Ser. No. 859,724, Sept. 22, 1969, Pat. No. 3,619,751.

Foreign Application Priority Data Sept. 27, 1968 Japan ..43/70673 Sept. 27, 1968 Japan ..43/70674 US. Cl ..318/325, 318/335 Int. Cl. ..H02p 5/16 Field of Search ..318/325, 335, 349, 481

[451 Oct. 17, 1972 [56] References Cited UNITED STATES PATENTS 3,463,990 8/l969 Ross ..318/3 35 3,086,238 4/1963 Baumhart ..318/349 Primary Examiner-Bernard A. Gilheany Assistant Examiner-Thomas Langer Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT 1 Claim, 10 Drawing Figures CROSS-REFERENCES TO RELATED APPLICATION This application is a continuation of copending Pat. application Ser. No. 859,724 filed on Sept. 22, 1969, now US. Pat. No. 3,619,751.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a motor speed controlling apparatus. I

' 2. Description of the Prior Art In the conventional apparatus for maintaining constant the rotating speed of an electric motor, such control is performed by actuating a mechanical switch provided in a power source circuit or by imparting a braking force to the rotary shaft of the electric motor. With such an arrangement, however, it is often the case that trouble occurs there due to faulty contacts and the regulated speed tends to change.

There is another example of such conventional apparatus, wherein on the basis of the fact that a voltage appearing across the terminals of the electric motor is proportional to the rotating speed of the motor (this condition is established in the case of no load), this voltage is compared with a reference voltage to detect a speed difference signal, and the resistance of a controlling transistor connected in series with a power source is controlled in accordance with a signal resulting from the detection, thereby controlling the current flow through the electric motor. This circuit is shown in FIG. 9, wherein M represents an electric motor to be controlled, and a' speed difference detecting bridge circuit is constituted by resistors R91, R92. R and M and Diodes D and D are connected across the opposite terminals of the electric motor. In this case, zener diodes are used for the diodes D and D and a voltage across them is utilized as the reference for the speed. The base of a transistor T is connected with the connection point between the resistors R and R the emitter of the transistor T is connected to the connection point between the resistors R and the diode D and the collector of the transistor T is connected to the base of a control transistor T of which the emitter and collector are connected in series with the electric motor M between the resistor R and a power source 13,. Thus, if the rotating speed of the electric motor M becomes higher than a predetermined value, then the voltage across the opposite terminals of the electric motor becomes higher than the reference voltage established by the diodes D and D so that the emitter voltage of the transistor T becomes higher than the base voltage thereof. As a result, the collector current of the transistor T decreases so that the resistance of the control transistor T is increased. Hence, the collector current of the transistor T flowing through the electric motor M via the resistor R is decreased. In this way, the speed of the motor is limited. On the other hand, if the motor speed becomes lower than the predetermined value, then it is increased by the reverse operation tothe above. However, this conventional system has such disa'dvantages that the control range with respect to load variations and voltage variations is narrow and hunting tends to occur due to brush noise. v e

2 SUMMARY OF THE INVENTION In accordance with the present invention, the foregoing drawbacks can be effectively removed.

It is an object of the present invention to provide a motor speed controlling apparatus wherein use is made of a pressure-sensitive element of which the electrical resistance or voltage developed thereacross is varied in accordance with a pressure imparted thereto, a centrifugal force occurring at a rotary member is imparted to the sensitive element, and a current flowing through the motor is controlled in accordance with the variation in the electric resistance of the sensitive element.

Another object of the present invention is to provide a motor speed controlling apparatus wherein there are provided ameans for producing a centrifugal force in accordance with the rotating speed of the motor and a sensitive element of which the electrical resistance or developed voltage is varied in accordance with the centrifugal force, and a current flowing through the motor is controlled in accordance with an unbalance current of a balanced bridge circuit including the sensitive element as one of the elements thereof, thereby controlling the electric motor at a constant speed.

Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 to 6 are circuit diagrams showing the motor speed controlling apparatus according to embodiments of the present invention, respectively.

FIGS. 7a and 7b are views useful for the speed de- DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described with reference to the drawings.

Referring first to FIG. 1, M, represents an electric motor to be controlled the rotor of which is provided with a .centrifugal force mechanism 1. There is provided an element 2 sensitive to a pressure or stress, e.g. a piezoelectric device, to which the centrifugal force of the mechanism 1 is applied. The sensitive element 2 has one end thereof connected with the base of a transistor T, of which the collector is connected with one of the terminals of the motor M,. The other end of the sensitive element 2 is connectedwith the other terminal of the motor M, through a variable resistor 3 for speed regulation, and a power source E, is connected between the other terminal of the motor M, and the emitter of the transistor T,. The sensitive element 2 may be one whose electrical resistance is varied upon application ,of a pressure thereto or one that a voltage produced thereby is varied upon application of a pressure thereto.

Referring now to FIG. 7a, there is schematically shown the aforementioned centrifugal force mechanism, wherein numeral 4 denotes a weight, and F indicates the centrifugal force and direction thereof.

The weight 4 is connected to the rotary shaft 6 of the motor M, by means of a spring 5, so that there is produced a centrifugal force which is proportional to the product of the square of rotating speed to and the weight m of the weight 4. As the rotating speed to increases, the weight 4 is brought closer to the sensitive element 2 by means of the centrifugal force. immediately before the speed 10 to which the motor is to be controlled is'reached, theweight 4 is brought into contact with the sensitive element 2. That is, the weight 4 is brought in contact with the sensitive element 2 at a point P slightly short of that corresponding to the rotating speed w as shown in FIG. 8. If it is assumed that the characteristic of the'sensitive element 2 beyond this point (variations in the resistance value r of the sensitive element with the rotating speed to) is represented by a straight line L, then the resistance value r when the control speed 0),, is reached corresponds to the resistance value of the sensitive element 2 at that point.

Description will now be made of the operation of the foregoing arrangement. Assume that as a result of an increase of the rotating speed (0 of the motor M, a pressure is imparted to the sensitive element 2 so that the resistance value r of the sensitive element 2 is increased along the straight line L shown in FIG. 8. Then, a base current I,,- which has been flowing through the emitter of the transistor T from the power source E is decreased, and collector current I is limited. Thus, the decrease of the current (namely, flowing through the motor M results in a decrease of the rotating speed w so that the resistance value r of the sensitive element 2 is concomitantly decreased along the straight line L. Consequently, the base current 1,, is again increased so that the collector current 1 is also increased, resulting in an increase of the rotating speed to of the motor M As will be appreciated from the foregoing, there is established a feedback system wherein the desired speed on, is adjusted by means of the variable resistor 3, the rotating speed 1 of the motor M which is an object to be controlled is detected by means of the sensitive element 2, and the base current l and in turn the collector current l of the transistor T is controlled in accordance with the resistance value r of the sensitive element, thereby controlling the rotating speed to of the motor M When a point q on the characteristic line of the sensitive element 2 or the desired rotating speed w is reached, the resistance value is balanced with the point corresponding to r as the equilibrium point. At this point, if the voltage of the power source E, is increased or decreased, then the equilibrium point q is slightly shifted so that the rotating speed can be made to fall within a predetermined range of variation. Then, resistors R R R and R operate as the standard of the rotating speed.

FIG. 2 shows a second embodiment of the present invention,which is a parallel control system. This parallel control. system shown in FIG. 2 operates in substantiallyfthe same: manner as the series control system I show-n in FlG. l in FIG. 2, asensitive element 22 is asso fatedwith aQcntrifugal force mechanism 21 in such amanner that the higher the speed of a motor M the lower-becomes the resistance gvalue r of the sensitive ele rnent22nlflG. 7b schematically shows the centrifugal force mechanism. In' FIG." "8;" tihe" relationship between the rotating speed and the're'si stance value of the sensitive element '22.is' shown by a straight line L. When the speed becomes higher than a predetermined level, a transistor T is rendered conductive so that a great voltage drop is developed across a resistor 27 connected in series with a power source B, so that the rotating speed in of the motor M, is decreased. Numeral 23 represents a variable resistor, 24 a weight, 25 a spring, and 26 a rotary shaft.

As described above, in accordance with the present invention, speed control is preformed by utilizing a pressure-sensitive element, without using any contacts. Thus, there is no possibility of trouble due to faulty contacts, and it is less likely that the regulated speed is varied, so that the life span of the present device can be widened and the operation thereof can be stabilized. Furthermore, since use is made of the resistance gradient of a sensitive element rather than the openingclosing operation of a switch, wherein a current is suddenlymade to flow when the speed exceeds a predetermined value while when the speed becomes lower than the predetermined value the current flow is immediately cut off as in the prior art, any infinitesimal rotational irregularity is momentarily fed back, thus resulting in a remarkable effect of restraining rotational irregularities. In the case where such rotational irregularities constitute no problem, it is possible, of course, to make the present apparatus operate in a manner similar to on-off operation.

FIG. 3 shows a third embodiment of the present invention, wherein M is an electric motor to be controlled the rotor of which is provided with a centrifugal force mechanism 31. There is provided an element 32 sensitive to a pressure to which the centrifugal force of the mechanism 31 is applied. A bridge circuit is constituted by the sensitive element 32, a reference voltage zener diode D (a reference voltage source such as a battery may be used in place of it), resistor R and I variable resistor 33. There is provided a transistor T having the base and the emitter thereof connected with the connection point between the diode D and the resistor R and that between the sensitive element 32 and the variable resistor 33 respectively. Further, resistors R and R are connected with the collector of the transistor T and the base of a control transistor T is connected with the connection point between the resistors R and R with the emitter and the collector of the transistor T being connected with a power source E .and the motor M, respectively. The resistance value r of the sensitive element 32 is decreased with an increase of the rotating speed of the motor M as shown by the straight line L in FIG. 8. It is assumed that the resistance value of the sensitive element 32 at a point q corresponding to the speed (0 to which the motor is to be controlled is r,,.

Description will now be made of the operation of the embodiment shown in FIG. 3. If the rotating speed to of the motor M is lower than ru 'then the resistance value r of the sensitive element 32 is so high that the emitter voltage of the transistor T is lower than the base voltage thereof so that a high collector current is permitted to flow through the transistor T via the resistors R and R 'Part of the collector current is supplied to the control transistor T as base current to decrease the impedance value of the transistor T so that an increased current is made to flow through the motor M As the rotating speed or increases, the resistance value r of the sensitive element 32 decreases along the straight line L so that the emitter voltage of the transistor T builds up. However, since the base voltage of the transistor T is maintained constant with the aid of the diode D the collector current thereof is decreased so that the base current of the transistor T is restricted. Thus, the impedance value of the transistor T increases. The result is that the current flowing through the motor M is limited so that the rotating speed to is decreased to be controlled to the preset value to If the voltage of the power source E is decreased due to consumption of the battery or the like, then the rotating speed of the motor M is decreased so that the resistance value of the sensitive element 32 is increased and the potential difference across the motor M is decreased, thus resulting in a great potential difference between the base and the emitter of the transistor T Thus, the collector current of the transistor T is increased to decrease the resistance between the emitter and the collector of the transistor T so that the voltage drop across the transistor T is decreased. In this way, any decrease in the voltage of the power source E is compensated for. The foregoing operation is possible only in the case where the base current of the transistor T is maintained constant. Therefore, the diode D is provided to serve as the reference for the power source voltage.

Next, description will be made of the embodiments shown in FIGS. 4 to 6. Basically, these embodiments operate in the same manner as the one shown in FIG. 3, although the former is slightly different from the latter in respect of their characteristics. In each of these embodiments, a centrifugal force produced by a centrifugal force mechanism associated with the rotor of an electric motor is imparted to a sensitive element, whereby the resistance value of the sensitive element is varied so that the balanced condition of a bridge circuit is changed to thereby control the speed of the motor. The speed reference depends upon the resistance value r r etc. of the aforementioned sensitive element. In FIG. 4, a resistor R. is coupled to a point where a controlled voltage appears or the collector of a transistor T Further, a starting resistor R is connected across the emitter and collector of the transistor T ln FIG. 5,

- a resistor R is connected in place of the zener diode D shown in FIG. 3, and a diode D and resistor R is connected in series across the opposite terminals of a power source E thereby making constant the voltage of the power source. With the arrangement of FIG. 5, the characteristic is greatly improved. However, since part of the operation performed by the diode D in FIG. 3 is to be performed by the diode D it is necessary to use a diode having a greater capacity as D The zener diode D is not essential to obtain exact speed control performance. In order to compensate for this, the arrangement of FIG. 6 has been devised. That is, in view of the fact that satisfactory speed control can be achieved only if the voltage imparted to the bridge cir-.

cuit is stabilized, a diode D is connected across the pair of terminals of the bridge circuit. Thus, the current flowing through the diode D may be low, and therefore the capacity thereof may be small. Furthermore, the sensitivity is improved by providing a second sensitive element 64 of wh'c the characteristic is the rev rsal of that of the sensitii/e element 62 as shown by t e straight line L in FIG. 8, in place of the resistor 64 shown in FIG. 5.

ln FIGS. 3 to 6, M M M and M, are electric motors, 31, 41, 51 and 61 indicate centrifugal force mechanisms, 32, 42, 52, 62 and 64 sensitive elements respectively, 33, 43, 53 and 63 variable resistors R R32, R33 R34, R41 R42! R487 R449 R51! R52 R53: R55, R56 R621 63 and ec resistors, 31 41, 52 and D62 diodes, T32, T41, T42, T51, T52, T61 and T62 transistors, and E E E and E power sources respectively.

As described above, in accordance with the present invention, a pressure-sensitive element is incorporated as one of the elements constituting a bridge circuit, thereby making it possible to perform speed control with a contactless arrangement. Thus, there is no possibility of trouble due to faulty contacts, and it is less likely that the controlled speed is changed. Consequently, the life span of the present apparatus can be widened, and the stability thereof can be improved. Furthermore, since the resistance value of the aforementioned sensitive element is utilized as the speed reference, it is not necessary to effect regulation by means of a centrifugal force spring and provide any constant power source for speed reference. The speed regulation can be performed by means of an external static circuit as drive the motor, whereby the speed regulation is more simply and shortly performed compared with motor having a conventional mechanical centrifugal switch which is adjusted little by little as stop the motor each time. Still furthermore, since there is provided the element for detecting variations in the power source voltage, control can be achieved with respect to not only load variations but also power source voltage variations. Thus, there is provided a greatly improved control apparatus according to the present invention.

We claim:

1. A motor speed controlling apparatus comprising:

centrifugal force means for producing a centrifugal force in accordance with the rotation of an electric motor;

a transistor connected between said electric motor and a power source for controlling the current supplied to said motor by said source;

bias means connected to said transistor for applying a bias current to said transistor, said bias means including a pressure sensitive element having an impedance which varies with the centrifugal force imparted thereto by said centrifugal forcemeans, wherein said bias current is varied in accordance with the variation of impedance of said pressuresensitive element to maintain the rotational speed of said motor substantially constant; and

static means independent of said centrifugal force means for varying said bias current to set the rotational speed of said motor at a predetermined value.

222g fireman S'IA'J.ES PATENT 012?](213 CERTHFECATE OF CORRECTEGN 3, 699,418 Dated October l7, 1. 72

Patent No.

InV nt r( Kaoru SASABE et a].

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected 'as eho'wn below:

On the title page, correct the application filing date to read April 30, 197i.

' Signed and sealed this 29th dayof May 1973,

(S Attest:

,EDWARD M.FLETCHER,JR. v ROBERT GOTTSCHALK Attesting Officer Commissioner, of Paten g ggg @Nmm S'iA'l.i3S PATENT OFFICE @ERTHTICKCIE OF CORRECTIQN Patent No. 699/418 Dated October l7, 1972 Inventor) Kaoru sAsABE et al It is certified that error appears in the above-idenci fi ed patent and that said Letters Patent are hereby corrected as shown below:

gym

On the ti x'cle page, correct the applic ation fil'ing date to read April 30, 1971 Signed and sealed this '291 ;h dayof May 1973,

Attest:

A EDWARD M.FLETCHER,JR. o "ROBERT GOTTSCHALK Attesting Officer Commissioner. of Paten 

1. A motor speed controlling apparatus comprising: centrifugal force means for producing a centrifugal force in accordance with the rotation of an electric motor; a transistor connected between said electric motor and a power source for controlling the current supplied to said motor by said source; bias means connected to said transistor for applying a bias current to said transistor, said bias means including a pressure sensitive element having an impedance which varies with the centrifugal force imparted thereto by said centrifugal force means, wherein said bias current is varied in accordance with the variation of impedance of said pressure-sensitive element to maintain the rotational speed of said motor substantially constant; and static means independent of said centrifugal force means for varying said bias current to set the rotational speed of said motor at a predetermined value. 